This invention relates to the field of process control and, more particularly, to digital fluid flow control apparatus.
Digital fluid flow control has been practiced for many years. A plurality of individually actuatable bistable, i.e., ON/OFF, valve elements are connected in parallel between an upstream manifold and a downstream manifold. The valve elements have orifices that are weighted in area, usually according to a geometric progression. By selectively opening and closing different combinations of valve elements, the fluid flow rate can be controlled over a wide range from zero to a maximum value. Typical digital fluid flow control apparatus is disclosed in U.S. Pat. No. 3,746,041, which is assigned to the assignee of the present application.
Because of the large number of bistable valve elements, digital fluid flow apparatus has many more parts than its analog counterpart. For this reason, it is important that these parts be readily accessible for inspection, cleaning, and repair, and that assembly of the parts be simplified. It is also advantageous to be able to take the parts off line for inspection, cleaning, or repair without taking the apparatus out of the fluid line in which it is operating. Further, it is desirable to have a single valve design that can be scaled to fluid lines having a wide range of diameters.
To facilitate manufacture, it is desirable that the valve body be capable of fabrication without necessity for welding or casting. Greater reliability can be achieved if the parts of such housing have face seals rather than piston seals.